The movement of goods by road vehicles, more particularly trucks, tractor trailers, and the like, entails both the loading and unloading of the vehicles under a variety of circumstances. Ideally, the vehicle will be backed to position the load bed immediately adjacent and at a common level with a loading dock for a quick transfer of the load either to or from the vehicle load bed, using such equipment as may be considered necessary, including forklifts, hand trucks, etc.
However, it is infrequent that the ideal coplanar relationship between a vehicle load bed and a loading dock is achieved. This is the case for any number of reasons including rutted, unlevel or uneven dock areas upon which the vehicle must be positioned, variations in loading dock heights, the use of high volume trailers with floor heights much lower than existing loading docks, and the use of lightweight, low profile tires. Such tires, recently introduced as an economy measure, tend to position the truck load beds or floors below the conventionally encountered loading docks.
Various means have been proposed to overcome level differentials between the load bed and the dock, including the use of makeshift ramps using loose wood planking or the like as may be available, or more elaborate systems wherein jacks are extended between the rear of the vehicle and the ground with the level of the vehicle adjusted or brought into alignment with the dock by a physical upward jacking or elevating of the entire vehicle. Neither of these proposals have been found particularly desirable. The ramp, depending upon the height differential, may itself be unsafe and difficult to negotiate. Similarly, the ramp may be incapable of accommodating the weight of the goods moving thereover. It would also be necessary that the ramp accommodate variations in height differentials as will be encountered between different trucks and loading docks.
The use of vehicle elevating jacks has the advantages of a wide range of adjustability for direct alignment of the load bed with the floor of the dock and direct transfer of goods therebetween, providing in effect a continuous floor area over which lift trucks, hand trucks and personnel can easily move. However, the use of such jacks, which normally raise the entire end of the vehicle and constitute the only ground engaging supports, introduces a dangerous degree of instability based upon a variety of factors including the weight of the vehicle, the weight of the goods being moved, reaction to movement of the load handling equipment repeatedly off and on the vehicle, and the condition of the jack supporting ground surface. .Iadd.In addition, extension of the jacks renders the vehicle immobile making it impossible to raise the vehicle prior to backing up to the loading dock thereby facilitating proper alignment of the load bed with the dock. Moreover, with the increased use of independent rail units to transport the trailer beds without the aid of a flatbed rail car, movement of the vehicle upon elevation of the load bed to engage the rail unit is necessary..Iaddend.